Bottom Line:
Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature.An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis.Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

ABSTRACTQuiescent endothelial cells (EC) regulate blood flow and prevent intravascular thrombosis. This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines. Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature. An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis. We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo. Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

Mentions:
Although no differences in cell surface expression of CD39 were observed by flow cytometry following HUVEC activation, we tested the hypothesis that ATPDase enzymatic function could be inhibited by direct exposure to reactive oxygen intermediates. We observed that exogenous systems that generated oxidative stress and resulted in EC membrane lipid peroxidation (data not shown) could, in turn, significantly inhibit ATPDase activity in vitro. The reduced capacity of EC directly perturbed by oxidative stress to express ATPDase activity was demonstrated by both TLC analysis of radiolabeled ADP hydrolysis and by estimation of phosphate release from supplemental ADP (Fig. 6 a; Mann Whitney Rank Sum Test, P = 0.002). Further, impressive evidence for the loss of ATPDase functional activity was also derived from the demonstration that EC exposed to oxidative stress rapidly became unable to inhibit platelet responses to ADP in vitro (Fig. 6 b).

Mentions:
Although no differences in cell surface expression of CD39 were observed by flow cytometry following HUVEC activation, we tested the hypothesis that ATPDase enzymatic function could be inhibited by direct exposure to reactive oxygen intermediates. We observed that exogenous systems that generated oxidative stress and resulted in EC membrane lipid peroxidation (data not shown) could, in turn, significantly inhibit ATPDase activity in vitro. The reduced capacity of EC directly perturbed by oxidative stress to express ATPDase activity was demonstrated by both TLC analysis of radiolabeled ADP hydrolysis and by estimation of phosphate release from supplemental ADP (Fig. 6 a; Mann Whitney Rank Sum Test, P = 0.002). Further, impressive evidence for the loss of ATPDase functional activity was also derived from the demonstration that EC exposed to oxidative stress rapidly became unable to inhibit platelet responses to ADP in vitro (Fig. 6 b).

Bottom Line:
Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature.An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis.Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.

ABSTRACTQuiescent endothelial cells (EC) regulate blood flow and prevent intravascular thrombosis. This latter effect is mediated in a number of ways, including expression by EC of thrombomodulin and heparan sulfate, both of which are lost from the EC surface as part of the activation response to proinflammatory cytokines. Loss of these anticoagulant molecules potentiates the procoagulant properties of the injured vasculature. An additional thromboregulatory factor, ATP diphosphohydrolase (ATPDase; designated as EC 3.6.1.5) is also expressed by quiescent EC, and has the capacity to degrade the extracellular inflammatory mediators ATP and ADP to AMP, thereby inhibiting platelet activation and modulating vascular thrombosis. We describe here that the antithrombotic effects of the ATPDase, like heparan sulfate and thrombomodulin, are lost after EC activation, both in vitro and in vivo. Because platelet activation and aggregation are important components of the hemostatic changes that accompany inflammatory diseases, we suggest that the loss of vascular ATPDase may be crucial for the progression of vascular injury.